[time-nuts] A comparison of the TAPR-TICC and BG7TBL FA1

[timeok at timeok.it]

   Hi Mark,

   the tests you did are between two different sources, so it is not a test that can determine the noise floor of the instruments under test.
   I understand that it is still a comparison on the field between the two measuring instruments,
   however I think it is interesting to have the noise floor of the test set because it is a reference absolute value.

   I enclose a plot I made about the n.f. of the TICC to which I inserted a 10MHz in the reference channel and in the measurement channel the same signal,

   divided up to 1PPS in the measurement channel.

   I believe that this is the only way to measure the noise floor.

   best regards,

   Luciano


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   Data Fri, 6 Sep 2019 20:05:57 +0000
   Oggetto [time-nuts] A comparison of the TAPR-TICC and BG7TBL FA1
   I did a comparison of the performance of the TAPR-TICC/TADD2-Mini divider and the BG7TBL FA1 frequency analyzer performance. The reference clock for both devices was a 5071A cesium. The device being tested was a Nortel NTPX GPSDO 10 MHz output. Attached are screen dumps of the two Lady Heather runs.

   The noisy orange plot in the TICC run is the measured frequency offset from 10 MHz. The noisy blue plot in the FA1 run is the measured frequency offset from 10 MHz. (Note the scale factor differences) Looking at the SPAN value (the difference between the max and min frequency measurements) shows that the FA1 noise level is around 4 times higher than the TICC. The FA1 ADEV measurements are around 3 time higher. The FA1 may be better than the TICC at lower (<50 second) tau, but I have no way to verify that. The FA1 screen dump includes a histogram of the frequency measurements.

   issue with the FA1 is that it seems to have an inherent frequency measurement bias of around -0.0002 Hz. See the "avg#" value in the lower left corner of the plot. I get nearly the same bias values when measuring 1, 5, and 10 MHz signals. (I added a setting in Lady Heather to specify a measurment bias correction value). It is interesting that the same -0.0002 Hz bias was present in the original BG7TBL GPSDO.

   TAPR TICC pros:
   high performance
   lots of measurement and configuration options
   open source design

   TAPR TICC cons:
   more expensive
   requires external dividers to measure frequency (and a second power supply)
   no case

   FA1 pros:
   inexpensive (around $100), decent bang for the buck
   no frequency divider needed, 1 .. 80 MHz range
   very simple operation (no configuration needed)
   nice small unit with an extruded metal case.

   FA1 cons:
   measures frequency (no way to test 1PPS signals)
   around 3X-4x less performance than the TAPR TICC.
   closed source "black box"
   inherent minor frequency measurement offset

   Lately BG7TBL has released the FA2. This appears to be similar to the FA1, but it has some VERY nice features including a basic 1 Hz .. 200 MHz range plus a 30:1 pre-scaler allowing measurements to 6 GHz. It as an LCD display, an internal (adjustable) OCXO and external freq ref input, reference output, selectable 0.1/1/10 second timebase. Costs around $120 (with power supply) If the FA2 measurement performance matches the FA1, it would be greatly preferable over the FA1. I have an FA2 the way.
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